In an experiment designed to mimic the conditions deep inside the icy giant planets of our solar system, scientists were able to observe "diamond rain" for the first time as it formed in high-pressure conditions. Extremely high pressure squeezes hydrogen and carbon found in the interior of these planets to form solid diamonds that sink slowly down further into the interior.

The glittering precipitation has long been hypothesized to arise more than 5,000 miles below the surface of Uranus and Neptune, created from commonly found mixtures of just hydrogen and carbon. The interiors of these planets are similar—both contain solid cores surrounded by a dense slush of different ices. With the icy planets in our solar system, "ice" refers to hydrogen molecules connected to lighter elements, such as carbon, oxygen and/or nitrogen.

In the experiment, they were able to see that nearly every carbon atom of the original plastic was incorporated into small diamond structures up to a few nanometers wide. On Uranus and Neptune, the study authors predict that diamonds would become much larger, maybe millions of carats in weight. Researchers also think it's possible that over thousands of years, the diamonds slowly sink through the planets' ice layers and assemble into a thick layer around the core.